Upstream gauge sensor, downstream absolute pressure sensor system

ABSTRACT

A method for estimating pressure surround an engine uses a gauge pressure sensor upstream of an orifice and an absolute pressure sensor downstream of the orifice. In particular, atmospheric pressure can be determined when flow through the orifice is below a predetermined threshold.

BACKGROUND OF INVENTION

1. Technical Field

The field of the invention relates to engine systems using pressuresensors. In particular, the field of the invention relates to systemsthat use a determination of barometric pressure.

2. Background of the Invention

In engine control systems, it is advantageous to provide an estimate ofatmospheric (barometric) pressure. Barometric pressure (BP) affectsengine exhaust back-pressure, which affects the residual burnt exhaustgas remaining in the cylinder at the close of the exhaust valve.Further, barometric pressure affects available manifold vacuum foroperating various accessories.

One method for estimating barometric pressure uses measured andpredicted mass airflow. In this system, a difference between these twovalues is first attributed to temperature, and the remaining differenceis attributed to a change in barometric pressure. Such a system isdescribed in U.S. Pat. No. 5,136,517.

The inventors herein have recognized several disadvantages with theabove system. In particular, such an estimation method can be expensiveto calibrate such that accurate measurements are provided over alloperation conditions. In addition, the inventors have recognized thatimproved engine control can be achieved if accurate barometric pressurereadings are provided throughout vehicle operation. Thus, even if aninitial accurate barometric pressure is available, it is difficult toprovide an accurate barometric pressure throughout vehicle operation.

SUMMARY OF INVENTION

The above disadvantages of prior approaches are overcome by a method forestimating atmospheric pressure surrounding an engine intake manifoldcoupled to an orifice, with a first gauge sensor coupled upstream of theorifice and a second absolute sensor coupled downstream of the orifice.The method comprises indicating whether flow through the orifice issubstantially zero; and determining atmospheric pressure based on theupstream gauge pressure sensor and the downstream absolute pressuresensor in response to said indication.

By using both a gage and an absolute pressure sensor, it is possible toprovide an accurate barometric pressure. Further, since such ameasurement can be made whenever flow is substantially zero, it ispossible to provide periodic updates during vehicle operation. Thus, inone example, where the flow is a recirculated exhaust flow, thebarometric pressure update can be provided during, for example, idling,or wide open throttle operation since EGR is typically discontinued inthese conditions. However, it should be noted that there are variousother methods for indicating when flow through the orifice issubstantially zero, such as, for example, based on operating condition,based on environmental conditions, or any other method. Further, itshould be noted that there are various ways to determine atmosphericpressure based on the upstream gauge pressure sensor and the downstreamabsolute pressure sensor. For example, atmospheric pressure can bedetermined base on the sum or difference between the upstream anddownstream sensor, or a mathematical relationship using both theupstream and downstream sensor can be used.

An advantage of the above aspect of the invention is improved enginecontrol, thus giving reduced emissions.

BRIEF DESCRIPTION OF DRAWINGS

The advantages described herein will be more fully understood by readingan example of an embodiment in which the invention is used to advantage,referred to herein as the Description of the Preferred Embodiment, withreference to the drawings wherein:

FIG. 1 is a block diagram of an engine in which the invention is used toadvantage;

FIG. 2 is a schematic diagram of the EGR system;

FIGS. 3-6 are a high level flowcharts of various routines forcontrolling EGR flow; and

FIGS. 7-8 are schematic diagrams of pressure sensors.

DETAILED DESCRIPTION

Internal combustion engine 10, comprising a plurality of cylinders, onecylinder of which is shown in FIG. 1, is controlled by electronic enginecontroller 12. Engine 10 includes combustion chamber 30 and cylinderwalls 32 with piston 36 positioned therein and connected to crankshaft40. Combustion chamber 30 communicates with intake manifold 44 andexhaust manifold 48 via respective intake valve 52 and exhaust valve 54.Exhaust gas oxygen sensor 16 is coupled to exhaust manifold 48 of engine10 upstream of catalytic converter 20.

Intake manifold 44 communicates with throttle body 64 via throttle plate66. Intake manifold 44 is also shown having fuel injector 68 coupledthereto for delivering fuel in proportion to the pulse width of signal(fpw) from controller 12. Fuel is delivered to fuel injector 68 by aconventional fuel system (not shown) including a fuel tank, fuel pump,and fuel rail (not shown). Engine 10 further includes conventionaldistributor less ignition system 88 to provide ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12. Inthe embodiment described herein, controller 12 is a conventionalmicrocomputer including: microprocessor unit 102, input/output ports104, electronic memory chip 106, which is an electronically programmablememory in this particular example, random access memory 108, and aconventional data bus.

Controller 12 receives various signals from sensors coupled to engine10, in addition to those signals previously discussed, including:measurements of inducted mass air flow (MAF) from mass air flow sensor110 coupled to throttle body 64; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling jacket 114; a measurement ofmanifold pressure (MAP) from manifold pressure sensor 116 coupled tointake manifold 44; a measurement of throttle position (TP) fromthrottle position sensor 117 coupled to throttle plate 66; and a profileignition pickup signal (PIP) from Hall effect sensor 118 coupled tocrankshaft 40 indicating and engine speed (N).

Exhaust gas is delivered to intake manifold 44 by a conventional EGRtube 202 communicating with exhaust manifold 48, EGR valve assembly 200,and EGR orifice 205. Alternatively, tube 202 could be an internallyrouted passage in the engine that communicates between exhaust manifold48 and intake manifold 44. Pressure sensor 206 communicates with EGRtube 202 between valve assembly 200 and orifice 205. Pressure sensor 207communicates with intake manifold 44. Stated another way, exhaust gastravels from exhaust manifold 44 first through valve assembly 200, thenthrough EGR orifice 205, to intake manifold 44. EGR valve assembly 200can then be said to be located upstream of orifice 205. Also, pressuresensor 206 can be either absolute pressure sensor 700 or a gaugepressure sensor 800, which are described later herein in FIGS. 7 and 8.Further, pressure sensor 207 can be either absolute pressure sensor 700or a gauge pressure sensor 800. Further yet, pressure sensor 206 can beabsolute pressure sensor 700, while pressure sensor 207 can be gaugepressure sensor 800.

Flow sensor 206 provides a measurement of manifold pressure (MAP) andpressure drop across orifice 205 (DP) to controller 12. Signals MAP andDP are then used to calculated EGR flow as described later herein withparticular reference to FIG. 3-5. EGR valve assembly 200 has a valveposition (not shown) for controlling a variable area restriction in EGRtube 202, which thereby controls EGR flow. EGR valve assembly 200 caneither minimally restrict EGR flow through tube 202 or completelyrestrict EGR flow through tube 202. Vacuum regulator 224 is coupled toEGR valve assembly 200. Vacuum regulator 224 receives actuation signal(226) from controller 12 for controlling valve position of EGR valveassembly 200. In a preferred embodiment, EGR valve assembly 200 is avacuum actuated valve. However, as is obvious to those skilled in theart, any type of flow control valve may be used, such as, for example,an electrical solenoid powered valve or a stepper motor powered valve.

Referring now to FIG. 3, a routine is described for feedback controllingexhaust gas recirculation according to the present invention.

First, in step 310, the most recent BP estimate (BP{circumflex over ()}) is read. The routine for updating the BP estimate is described laterherein with particular reference to FIG. 4.

Next, in step 312, the routine determines the absolute pressure upstreamof orifice 205. In particular, the absolute pressure upstream of orifice205 is determined based on the sum of the most recent BP estimate andthe measured gauge pressure upstream of orifice 205. Further, thisupstream absolute pressure is clipped to be at least greater than theabsolute pressure measured by the absolute pressure sensor downstream oforifice 205. Further, if it is necessary to clip the values, thisindicates that the estimate of barometric pressure has degraded. Thus,according to the present invention, when this clipping occurs, thedesired EGR flow is set to zero so that the barometric pressure can beupdated as described later herein with particular reference to FIG. 4.

Next, in step 314, the EGR flow is determined based on the upstreamabsolute pressure and downstream absolute pressure using function ƒ. Inone aspect of the present invention, function ƒ is structured so thatEGR flow is calculated based on the square root of the product ofdownstream absolute pressure and differential pressure across orifice205.

Then, in step 316, feedback EGR control is performed based on a desiredEGR flow and the calculated EGR flow from step 314.

Referring now to FIG. 4, a routine is described for estimatingatmospheric pressure, or barometric pressure, during vehicle operation.

First, in step 410, a determination is made as to whether the engine isstopped. This can be determined by, for example, determining whether theignition key is on, whether engine rpm is zero, or whether engine speedis zero for a predetermined duration, or whether engine fuel injectionis zero, or various other parameters that indicate that the engine isstopped. When the answer to step 410 is yes, the routine continues tostep 412.

In step 412, the routine updates the BP estimate based on the measuredabsolute pressure downstream of orifice 205, which in this embodiment isalso the manifold absolute pressure. In other words, when the engine isstopped, the routine determines absolute barometric pressure based onthe measured manifold pressure, or pressure downstream of orifice 205.

Then, in step 414, the old barometric pressure is set equal to the mostrecently updated barometric pressure.

When the answer to step 410 is no, the routine continues to step 416,where a determination is made as to whether the EGR flow issubstantially equal to zero. There are various methods for determiningwhether EGR flow is equal to zero such as, for example, determiningwhether the EGR valve is closed, determining whether the duty cyclecommand to the EGR valve is zero, determining whether the pressureupstream of the orifice is approximately equal to pressure downstream ofthe orifice, or any other parameter that indicates that EGR flow issubstantially equal to zero. Further, the definition of “substantially”equal to zero is when the indication of flow based on the pressuresensors is equal to a value that would be caused by noise on the sensorsduring engine operation. For example, the flow is substantially zerowhen the flow indicated is less that 10% of the maximum flow through thesystem during the present engine operating conditions. Also, pressureupstream is approximately equal to pressure downstream of the orificewhen, for example, the pressure values are within 10% of each other.However, this depends on the accuracy of the sensor and the amount ofnoise that is generated during the present engine operating conditions.When the answer to step 416 is yes, the routine continues to step 418.

In step 418, the barometric pressure estimate updated using a low passfilter in the equation in the Figure. In other words, when the EGR flowis zero, the absolute pressure upstream of orifice 205 is substantiallyequal to the absolute pressure downstream of orifice 205 since there isno flow. Thus, the absolute pressure measurement of the downstreampressure can be used in conjunction with the gauge pressure measurementupstream of orifice 205 to determine the reference pressure to the gaugesensor. In this example, the reference pressure to the gauge pressuresensor, which measures the gauge pressure upstream of orifice 205, isatmospheric pressure. Thus, according to the present invention, when EGRflow is zero, it is possible to accurately measure the atmosphericpressure using both the gauge and absolute pressure sensors coupledupstream and downstream of orifice 205.

When the answer to step 416 is no, the barometric pressure estimate isnot updated via the absolute pressure measurement downstream of orifice205, but is set equal to the old BP estimate value. However, in analternative embodiment, other estimates can be used at this time toprovide an estimate of barometric pressure. For example, the engine massairflow sensor and throttle position can be used to estimate barometricpressure. Thus, according to the present invention, a routine isdescribed that can provide online estimates of atmospheric pressureduring vehicle driving conditions when the EGR flow is equal to zerousing an upstream gauge pressure sensor and a downstream absolutepressure sensor.

Referring now to FIG. 5, a routine is described for default operation ofan engine EGR system having an upstream gauge pressure sensor and adownstream absolute pressure sensor.

First, in step 510 a determination is made as to whether the gaugepressure sensor has degraded. When the answer to step 510 is yes, theroutine continues to step 512. For example, sensor voltage can becompared to an allowable range. If sensor voltage is outside of theallowable range, degradation can be indicated. Further, an estimate ofthe sensor value can be obtained using other engine operating parametersand then compared with the sensor reading. If this comparison gives adifference that is greater than an allowable value, degradation isindicated.

In step 512, the routine discontinues EGR flow and controls fuelinjection based on the absolute pressure measurement downstream oforifice 205 (manifold pressure). In other words, the routine calculatesthe fuel injection amount based on speed density equations that relateair induction amount to manifold pressure and engine speed and enginemanifold temperature. In this way, it is possible to continue engineoperation even when upstream gauge pressure sensor has degraded.

When the answer to step 510 is no, a determination is made in step 514as to whether downstream absolute pressure sensor has degraded. When theanswer to step 514 is yes, the routine continues to step 516. Forexample, sensor voltage can be compared to an allowable range. If sensorvoltage is outside of the allowable range, degradation can be indicated.Further, an estimate of the sensor value can be obtained using otherengine operating parameters and then compared with the sensor reading.If this comparison gives a difference that is greater than an allowablevalue, degradation is indicated.

In step 516, the routine discontinues EGR flow and controls fuelinjection amount based on the gauge pressure sensor and the most recentbarometric pressure estimate. In other words, when EGR flow is zero, theabsolute pressure upstream of orifice 205 is approximately equal to theabsolute pressure downstream of orifice 205. Thus, by using the gaugepressure upstream of orifice 205 and the most recent estimate ofbarometric pressure, it is possible to estimate an absolute pressuredownstream of orifice 205 (estimated intake manifold pressure). Then,this estimated manifold pressure can be used with the speed densityfunctions to calculate a proper fuel injection amount. Thus, accordingto the present invention, it is possible to continue accurate engineoperation of a system having an upstream gauge pressure sensor and adownstream absolute pressure sensor, when the downstream absolutepressure sensor has degraded.

Referring now to FIG. 6, a routine is provided for default operation ofan engine EGR system having two absolute pressure sensors, one upstreamof orifice 205 and one downstream of orifice 205.

First, in step 610, a determination is made as to whether eitherabsolute pressure sensor is degraded. When the answer to step 610 isyes, the routine discontinues EGR and controls fuel injection amountbased on the absolute pressure sensor that has not degraded. In otherwords, when EGR flow is zero, both absolute pressure sensors should bereading approximately the same absolute pressure. Thus, the routine useswhichever sensor has not degraded to provide the fuel injection control.

While various methods can be used to determine whether a pressure sensorhas degraded, one potential method is to determine whether the voltageoutput is within acceptable predetermined voltage limits. Thus, if thevoltage read by the sensor is outside of this acceptable output range,degradation can be indicated. However, there are various other methodsfor determining degradation such as using other engine operatingparameters to estimate the pressure, and indicating degradation whenthese values disagree by a predetermined amount.

In an alternative embodiment, the present invention can be utilized witha hybrid electric vehicle system. In this system, an engine and anelectric motor are coupled to the vehicle. In some operating modes, boththe engine and the electric motor drive the vehicle. In other operatingmodes, only the engine or only the electric motor drive the vehicle. Instill other operating modes, the engine drives the electric motor torecharge a battery system. According to the present invention, it ispossible to update a barometric pressure estimate when the vehicle isdriven by the electric motor and the engine is stopped (see step 410 ofFIG. 4). In other words, estimates of barometric pressure can beobtained while the vehicle is operating under the pure electric mode andthe engine is stopped. Thus, it is possible to provide continuingupdates in barometric pressure using a manifold absolute pressuresensor.

Referring now to FIG. 7, a schematic diagram of an absolute pressuresensor is described. In particular, absolute pressure sensor 700, whichis coupled to engine intake manifold 44, is described. Absolute pressuresensor 700 comprises a base structure 705, which supports the pressuresensor elements as described below. Coupled to base 705 is supportmember 710. Support member 710 is comprised of silicon. Support member710 has a sealed vacuum reference chamber 720 within. Vacuum referencechamber serves as a regulated reference pressure so that sensor 700 canprovide an indication of absolute pressure sensor regulated referencepressure is known and fixed. Coupled to support 710 are aluminumconductors and an electronics layer 730. This aluminum conductor andelectronics layer 730 contains sensitive electronic components thatconvert the applied pressure and the vacuum reference into electricalsignals provided to controller 12. A nitride layer 740 is coupled on topof aluminum conductor and electronics layer 730. Also, gold wire bonds780 connect the aluminum conductor and electronics layer 730 to base705. A gel layer 760 surrounds the aluminum conductor and electronicslayer 730, nitride layer 740, support 710, vacuum reference 720, andgold wire bonds 780. The pressure to be measured is applied to gel layer760. Gel layer 760 protects the sensitive electronics in layer 730 fromthe gases creating the applied pressure.

The inventors herein have recognized that while it is possible tomanufacture a gel layer, which can protect the electronics from hotexhaust gases containing various contaminants, this can be an expensiveapproach. Thus, according to the present invention, absolute sensor isused to measure intake manifold pressure, which is comprised primarilyof fresh air inducted past throttle plate 66 from the atmosphere. Thus,a relatively inexpensive gel layer 760 can be utilized and exploited.Thus, while it is possible to use an absolute sensor such as describedabove to measure exhaust pressures, it is also desirable to providealternative methods and systems that do not rely solely on absolutepressure sensors.

Referring now to FIG. 8, gauge pressure sensor 800 is described. In thisparticular embodiment, gauge pressure sensor 800 is measured relative toatmospheric pressure. However, various other reference pressures may beused. Base 800 is shown coupled to support 810. Support 810 is comprisedof silicon. Aluminum conductors and electronics layer 830 is coupled toone side of support 810. The opposite side of support 810 is constructedso that the measured, or applied, pressure is in contact with support810.

As above, aluminum conductors and electronics layer 830 comprisesensitive electronic components. Nitride layer 840 is coupled toaluminum conductors and electronics layer 830. Also, diaphragm 850 iscoupled within nitride layer 840 and coupled to aluminum electronicslayer 830. Atmospheric pressure is applied to diaphragm 850 and nitridelayer 840. Gold wire bonds 880 couple aluminum electronics layer 830 tobase 800.

The inventors herein have recognized that gauge pressure sensor 800 doesnot suffer from the disadvantages suffered by absolute sensor 700 withrespect to the requirements for gel layer 760. In other words, withgauge pressure sensor 800, it is possible to measure exhaust pressure asthe applied pressure, without adding expensive gels to protect thesensitive electronics in the layer 830.

Thus, according to the present invention, a method is described forcontrolling exhaust gas recirculation using an absolute sensor tomeasure intake manifold pressure (which does not require expensive gelssince intake manifold pressure gases are at a lower temperature and haveless contaminants than exhaust pressure gases) and a gauge pressuresensor to measure a pressure of recycled exhaust gases (which can be ata higher temperature and have various contaminants). In other words,gauge pressure sensor 800 can be manufactured cheaply and provide usefulmeasurements of recycled exhaust gases. Thus, according to the presentinvention, a reduced cost system can be provided.

Although several examples of the invention have been described herein,there are numerous other examples which could also be described. Forexample, the invention can also be used with various types of emissioncontrol devices such as so-called lean burn catalysts. Further, theimproved barometric pressure estimate can be used in other enginecontrol systems. For example, the improved barometric pressure estimatecan be used in scheduling engine actuators and desired engine operatingpoints. In particular, the improved barometric pressure estimate can beused in determining a desired EGR flow, or EGR valve, set-point. Then,the measured, or estimated EGR flow value can be used in a feed-backcontrol scheme so that the actual EGR flow, or valve position,approaches the set-point value. Further, the improved barometricpressure estimate can be used in determining a ignition timingset-point. In other words, desired ignition timing can be varied basedon the determined barometric pressure.

What is claimed is:
 1. A system through which gasses flow comprising: anorifice located in the gas flow; a first gauge pressure sensor measuringpressure relative to atmospheric pressure coupled upstream of theorifice; a second absolute pressure sensor coupled downstream of theorifice; and a valve coupled upstream of said orifice; a computerstorage medium having a computer program encoded therein for estimatingatmospheric pressure surrounding the system, said computer storagemedium comprising: code for indicating whether flow through the orificeand valve is less than a predetermined value; and code for determiningatmospheric pressure based on said upstream gauge pressure sensor andsaid downstream absolute pressure sensor in response to said indication.2. The system recited in claim 1 wherein said computer storage mediumfurther comprises code for calculating flow through the orifice andvalve based on said upstream gauge pressure sensor, said downstreamabsolute pressure sensor, and said determined atmospheric pressure. 3.The system recited in claim 1 wherein said computer storage mediumfurther comprises code for adjusting said valve based on said calculatedflow.
 4. The system recited in claim 1 wherein said orifice is coupledto an engine.
 5. The system recited in claim 1 wherein the flow isexhaust gas recirculation.
 6. An article of manufacture comprising: acomputer storage medium having a computer program encoded therein forestimating atmospheric pressure surrounding an engine intake manifoldcoupled to an orifice, with a first relative sensor coupled upstream ofthe orifice and a second absolute sensor coupled downstream of theorifice, said relative sensor sensing a pressure relative to anunregulated reference pressure, said absolute sensor sensing pressurerelative to a regulated reference pressure, said computer storage mediumcomprising: code for indicating whether flow through the orifice is lessthan a predetermined value; and code for determining atmosphericpressure based on the upstream relative pressure sensor and thedownstream absolute pressure sensor in response to said indication.
 7. Amethod for estimating pressure surrounding an orifice, with a firstsensor coupled upstream of the orifice and a second sensor coupleddownstream of the orifice, comprising: indicating whether flow throughthe orifice is less than a preselected amount; and calculating thesurrounding pressure based on a first signal from the first sensorindicative of pressure relative to said surrounding pressure and asecond signal from the second pressure sensor indicative of pressurerelative to a known pressure, in response to said indication.
 8. Amethod for estimating atmospheric pressure surrounding an engine intakemanifold coupled to an orifice, with a first gauge sensor coupledupstream of the orifice and a second absolute sensor coupled downstreamof the orifice, comprising: indicating whether flow through the orificeis less than a preselected amount; measuring a first pressure relativeto atmospheric pressure from the first gauge sensor; measuring a secondpressure from the second absolute pressure sensor; and determiningatmospheric pressure based on said first measured pressure and saidsecond measured pressure in response to said indication.
 9. The methodrecited in claim 8 further comprising determining an engine set-pointbased on said determined atmospheric pressure.
 10. The method recited inclaim 8 wherein said indication is provided in response to a controlvalve coupled to the orifice being closed.
 11. The method recited inclaim 8 wherein said indication is provided in response to a controlvalve coupled to the orifice being commanded to close.
 12. The methodrecited in claim 8 wherein said indication is provided in response tothe engine idling.
 13. The method recited in claim 8 wherein saidindication is provided in response to pressure upstream of the orificebeing approximately equal to pressure downstream of the orifice.
 14. Themethod recited in claim 6 wherein said determining atmospheric pressurefurther comprises determining atmospheric pressure based on a comparisonof said first measured pressure and said second measured pressure. 15.The method recited in claim 8 wherein the flow is an exhaust gasrecirculation flow.
 16. The method recited in claim 8 wherein the flowis controlled by a flow control valve coupled upstream of the orifice.